The present invention relates to a thin-film capacitor and a method for fabricating the thin-film capacitor, and an electronic device and a circuit board.
Generally, decoupling capacitors are mounted near an LSI (Large Scale Integrated circuit), etc. mounted on a printed circuit board so as to prevent erroneous operations due to source voltage variations and radio-frequency noises.
The decoupling capacitors are formed on a substrate which is separate from the printed circuit board and are mounted suitably on the printed circuit board.
Recently, as the LSI, etc. have the operation speed increased and the electric power consumption decreased, the decoupling capacitors are required to have the characteristics improved. As the LSI, etc. are downsized, the decoupling capacitors are required to be downsized.
Then, techniques for satisfying the requirement of downsizing the decoupling capacitors while increasing the capacitance are proposed.
A proposed capacitor will be explained with reference to FIG. 35. FIG. 35 is a sectional view of the proposed capacitor.
As illustrated in FIGS. 22A and 22B, a silicon oxide film 112 is formed on a silicon substrate 110. On the silicon oxide film 112, capacitor electrode (lower electrodes) 114 of, e.g., a 100 nm-thickness Pt film are formed. On the capacitor electrodes 114, a 100 nm-thickness capacitor dielectric film 116 is formed of, e.g., a BaXSr1-XTiO3 film (hereinafter also called “BST film”), which is a high dielectric substance. On the capacitor dielectric film 116, capacitor electrodes (upper electrodes) 118 of a 100 nm-thickness Pt film are formed. Thus, capacitor parts 120 are formed each of the capacitor electrode 114, the capacitor dielectric film 116 and the capacitor electrode 118.
On the silicon substrate 110 with the capacitor parts 120 formed on, an insulating barrier film 122 is formed. The insulating barrier film 122 is for preventing hydrogen or water from arriving at the capacitor parts 120.
That is, in fabricating or using the thin-film capacitors, when hydrogen or water arrive at the capacitor dielectric film 116, there is a risk that the oxide forming the capacitor dielectric film 116 may be reduced with the hydrogen, and the electric characteristics of the capacitor parts 120 may be deteriorated. In the thin-film capacitor illustrated in FIG. 22, the insulating barrier film 122 is formed, covering the capacitor parts 120, whereby the hydrogen or water are prevented from arriving at the capacitor dielectric film 116.
On the insulating barrier film 122, a protection film 130 of, e.g., a resin is formed. In the protection film 130 and the insulating barrier film 122, openings 132a and openings 132b are formed respectively down to the capacitor electrodes 114 and the capacitor electrodes (upper electrodes) 118. Electrodes 134a, 134b for the connection to the outside are buried respectively in the openings 132a, 132b. Solder bumps 136 are formed on the outside connection electrodes 134a, 134b. 
The capacitor electrodes 114 of the capacitor parts 120 are electrically connected to the power source line of, e.g., the circuit board (not illustrated) via the outside connection electrodes 134a and the solder bumps 136. The capacitor electrodes 118 of the capacitor parts 120 are electrically connected to the ground line of, e.g., the circuit board (not illustrate) via the outside connection electrodes 134b and the solder bumps 136.
The thin-film capacitor illustrated in FIGS. 22A and 22B has the capacitor dielectric film 116 which is formed of the high dielectrics and is formed as thin as about 100 nm, and the capacitance can be improved. Furthermore, the thin-film capacitor can be formed by the semiconductor process, and can be formed, micronized. The inductance can be decreased. Thus, the proposed thin-film capacitor can surely prevent the source voltage variation, and can sufficiently remove the radio-frequency noises.
Following references disclose the background art of the present invention.
[Patent Reference 1]
Specification of Japanese Patent Application Unexamined Publication No. Hei 11-97289
[Patent Reference 2]
Specification of Japanese Patent Application Unexamined Publication No. 2000-228499
[Patent Reference 3]
Specification of Japanese Patent No. 3157734
[Patent Reference 4]
Specification of Japanese Patent Application Unexamined Publication No. Hei 9-293869
[Patent Reference 5]
Specification of Japanese Patent Application Unexamined Publication No. 2002-110931
However, in the thin-film capacitor illustrated in FIGS. 22A and 22B, the hydrogen or water cannot be prevented from arriving at the capacitor dielectric film 116 via the outside connection electrodes 134a, 134b. The capacitor dielectric film 116 is reduced to some extent, and sufficiently satisfactory electric characteristics cannot be always obtained.